This invention relates to methods of reinforcing a fibrous roller cladding material, to reinforced roller cladding and to clad lehr rollers wherein the cladding comprises reinforced fibrous material.
When flat glass is produced continuously, for example by a float or rolled process, a continuous ribbon of glass is formed that is annealed to remove stresses before being cut into sheets. The ribbon of hot glass is typically conveyed on a roller bed through a lehr where the glass passes through different temperature zones to anneal and cool the glass. Rollers made of different materials are used in different parts of the roller bed. Clad lehr rollers are commonly used in those areas of the lehr where the temperature is in the range 200° C. to 700° C.; more usually where the temperature is in the range 200° C. to 550° C. A clad lehr roller comprises a central shaft often made from steel with an outer cladding of a material having a low thermal conductivity which is sufficiently robust to withstand the high temperatures and which will not mark the surface of the glass. Over recent years millboard has replaced asbestos board as the cladding material of choice. Millboard is a monolithic fibre board made of ceramic or mineral fibres, inert fillers and small amounts of organic binders. Typically a clad lehr roller comprises a cladding formed from a plurality of millboard disks, each disk having a hole punched in the centre and all the disks being mounted on a shaft and held under lateral compression. Alternatively the cladding could comprise a number of hollow cylinders or a single hollow cylinder mounted upon the shaft.
A problem with millboard is that it is not as resistant to abrasion as asbestos and consequently clad lehr rollers comprising a millboard cladding are more vulnerable to cullet damage and to cullet becoming embedded in the cladding. The term cullet used herein refers to broken flat glass. Cullet damage can occur when the clad roller rotates and cullet in contact with the surface of the cladding gouges out channels in that surface thereby reducing the useful life of the roller. Cullet damage also releases millboard particles into the atmosphere which may settle on the glass surface and reduce its quality. In addition, pieces of cullet can become embedded in the cladding and mark the surface of glass thereby reducing the quality of the glass. Replacing a damaged roller increases maintenance costs and can disrupt the glass manufacturing process. There is a need for a clad lehr roller which is less susceptible to damage and thereby has a longer useful life.
U.S. Pat. No. 3,763,533 discloses processes in which mineral fibres such as kaolin wool, glass wool, rockwool and slag wool were bound using a liquid binder such as colloidal silicic acid or solutions of silicates and phosphates such as monoaluminium phosphate to form a roller cladding material. Strips of fibre were felt wound around a roller core, impregnated with a binder and heated until dry. Such rollers have proven not to be sufficiently acceptable to find wide use in replacing asbestos rollers.
U.S. Pat. No. 5,378,219 describes a roller cladding material in the form of a compressed fibre roll cover which may comprise a binder such as colloidal silica or colloidal alumina. The fibre roll may be impregnated with a suspension of the binder and dried.
U.S. Pat. No. 4,216,005 disclosed asbestos rolls for use in the conveying of heated glass that have been chemically treated with an aqueous solution of potassium sulphate. The material with which the roll is treated permeates the asbestos and crystallises upon drying, and the crystals serve to bind the asbestos particles together to form a cohesive mass.
JP 09048628A discloses rollers for transporting flat glass. The rollers have a cladding made from discs of inorganic fibres which have been dipped in an aqueous solution of saturated potassium sulphate at greater than 50° C. for less than 1 hour under a reduced or pressurised state to penetrate potassium sulphate into an outer peripheral part of the disc. The discs are subsequently removed from the solution and dried.
Applicants have discovered that a clad roller having an extended useful lifetime may be produced by contacting a surface of the cladding with a fluid medium comprising a reinforcing agent and drying the material to produce a roller with a harder surface.